In a 5-4 decision the court said that the coverage formula used by the government to determine which states are required to get federal permission before they make any changes to voting laws is unconstitutional. The ruling effectively puts the issue back in the hands of lawmakers to revise the law. And until then, the ruling effectively renders section five of the Voting Rights Act inoperable.

"Our country has changed, and while any racial discrimination in voting is too much, Congress must ensure that the legislation it passes to remedy that problem speaks to current conditions," wrote Chief Justice John Roberts in the court's opinion.

The decision came down along partisan lines, with conservative justices Roberts, Antonin Scalia, Anthony M. Kennedy, Clarence Thomas, and Samuel Alito making up the majority.

The court left standing Section 5 of the law, a key section that requires states with a history of voter discrimination to have any changes to voting rules approved by federal officials, but strikes down the coverage formula used to choose which states should be covered.

"We issue no holding on section 5 itself, only on the coverage formula. Congress may draft another formula based on current conditions," Roberts said.

Justice Ruth Bader Ginsburg wrote a dissent joined by Justice Kagan, Breyer, and Sotomayor.

"Just as buildings in California have a greater need to be earthquake-proofed, places where there is greater racial polarization in voting have a greater need for prophylactic measures to prevent purposeful race discrimination," Ginsburg took the unusual step of reading her dissent from the bench.

Critics say that Congress ignored prior warnings from the Court about the continued constitutionality of some sections of the law.

"If Congress had updated the coverage formula to use registration and turnout data from the 2004 election, none of the states currently subject to Section 5 would have remained covered because the registration and turnout of black voters is on par with white voters and exceeds that of white voters in some of the covered states," said Hans von Spakovsky, senior legal fellow at the Heritage Foundation. "It is a victim of its own success and is no longer needed. Despite claims to the contrary, Americans will continue to be protected from discrimination by the other permanent provisions of the Voting Rights Act."

Supporters of the law fear that Congress—with its deepening partisan divide-- will not act.

Jon Greenbaum, chief counsel of the Lawyers' Committee for Civil Rights Under Law expressed dismay.

"The Supreme Court has effectively gutted one of the nation's most important and effective civil rights laws," Greenbaum said. "Minority voters in places with a record of discrimination are now at greater risk of being disenfranchised than they have been in decades. Today's decision is a blow to democracy. Jurisdictions will be able to enact policies which prevent minorities from voting, and the only recourse these citizens will have will be expensive and time-consuming litigation."